1. Field
The present invention relates to a lithographic apparatus and a method for manufacturing a device.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate (e.g., a silicon wafer or a glass plate, having a substantially circular shape or a polygonal shape, e.g., a rectangular shape). A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, that is alternatively referred to as a mask or a reticle, can be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) on a substrate.
Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned.
Conventional lithographic apparatus include so-called steppers, in that each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in that each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction), while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
Instead of a mask, the patterning device can comprise a patterning array that comprises an array of individually controllable elements, like a programmable mirror array or a programmable LCD array. Such a system, compared to a mask-based system, allows the pattern to be changed more quickly and for much less cost because the mask configuration exists in software only.
Instead of a circuit pattern, the patterning device can be used to generate other patterns, for example a color filter pattern or a matrix of dots, for a flat panel display. A flat panel display substrate can be rectangular in shape. Lithographic apparatus designed to expose a substrate of this type can provide an exposure region that covers a full width of the rectangular substrate, or that covers a portion of the width (for example, half of the width). The substrate can be scanned underneath the exposure region, while the mask or reticle is synchronously scanned through the projection beam. In this way, the pattern is transferred to the substrate. If the exposure region covers the full width of the substrate, then exposure can be completed with a single scan. If the exposure region covers, for example, half of the width of the substrate, then the substrate can be moved transversely after the first scan, and a further scan is typically performed to expose the remainder of the substrate.
Conventionally, a substrate is supported on a substrate support (also called a substrate stage), and a suitable drive is coupled to the substrate support for moving it in several degrees of freedom, e.g., in X, Y and Z directions and in Rx, Ry, and Rz directions when considering an XYZ system of coordinates. Reaction forces that are generated while moving the substrate support are transferred to a machine frame on that the substrate support is movably mounted, e.g., on air bearings.
The machine frame can contain a light source and the projection optics jointly generating a patterned radiation beam to be imaged on a substrate in the lithographic apparatus. The substrate must be positioned with high accuracy, in particular in an XY plane, with respect to the radiation beam.
When sizes of substrates increase, generally also the substrate support's dimensions grow larger, while at the same time its mass increases to maintain a required dimensional stability, both static and dynamical. As an example, a substrate having an increased size is a flat panel display substrate. Moving a relatively large mass substrate support with high speed requires high forces to be generated by the substrate support drive, whereas at the same time a high position accuracy is mandatory.
Controlling the position of the substrate support relative to the machine frame with a high accuracy implies that the substrate support drive has a relative large servo bandwidth, e.g., about 50 Hz. However, the substrate support position control bandwidth is limited by internal dynamics of the substrate support, and more particularly by the internal dynamics of the machine frame and the projection optics. Since the machine frame and the projection optics have a high mass, the internal dynamics of these components cannot be designed with a high eigen frequency that would enable a large substrate support position control bandwidth, resulting in an unacceptable substrate support performance.
Therefore, what is needed is a system and method that increase a substrate support position control bandwidth, such that a substrate support having a high mass can be positioned with a high accuracy.